Aerodynamically active stiffening feature for gas turbine recuperator

ABSTRACT

A method of manufacturing a recuperator disposed in the exhaust duct of a gas turbine engine includes forming a first leading recess adjacent a leading edge of a first thermally conductive sheet and forming a second leading recess adjacent a leading edge of a second thermally conductive sheet, the first and second thermally conductive sheets forming components of a recuperator plate. The first leading recess of the first thermally conductive sheet is mated with the second leading recess of the second thermally conductive sheet, and then the first and second leading edges are joined thereby forming a recuperator plate. The first and second leading recesses form a trough extending along a leading edge of the recuperator plate in a direction substantially parallel to a longitudinal axis of the recuperator plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser. No. 13/804,118 filed Mar. 14, 2013, the entire contents of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to gas turbine engines and more particularly to recuperators for such gas turbine engines.

BACKGROUND

A recuperator may be used to effect heat exchange in a gas turbine engine. A high performance recuperator typically needs a large number of recuperator plates made from thin foil, positioned relative to one another with high accuracy. In particular, a pair of sheets are generally joined together to form each recuperator plate and precise positioning of the two sheets is desired when assembling them into the plate. However, due to the small features of each sheet, such positioning precision may be difficult to achieve.

Conventional assemblies tend to rely on trimming the edges of the sheets to position the latter. This may result in the plates becoming wavy during the press forming of each recuperator plate, thereby reducing the accuracy in the relative positioning of the sheets. As a result, the overall performance of the recuperator is negatively effected.

There is therefore a need for improved gas turbine engine recuperators.

SUMMARY

In one aspect, there is provided a method for manufacturing a recuperator for a gas turbine engine, the method comprising: forming at least one recuperator plate, the recuperator plate extending in a longitudinal direction between an upstream and a downstream end spaced apart along a longitudinal axis, the recuperator plate extending in a transverse direction between a leading edge and a trailing edge thereof, each of the leading edge and the trailing edge extending longitudinally between the upstream and the downstream edges, the transverse direction being substantially perpendicular to the longitudinal direction defined by the longitudinal axis, forming the recuperator plate including: providing first and second thermally conductive sheets, respectively having a first sheet leading edge and a first sheet trailing edge, and a second sheet leading edge and a second sheet trailing edge; forming a first leading recess adjacent the first sheet leading edge of the first thermally conductive sheet, and forming a second leading recess adjacent the second sheet leading edge of the second thermally conductive sheet; mating the first leading recess of the first thermally conductive sheet with the second leading recess of the second thermally conductive sheet; and following the step of mating, joining the first and second thermally conductive sheets together to form the recuperator plate with at least one fluid channel therein, the mated first and second leading recesses forming a trough extending along a leading edge of the recuperator plate in a direction substantially parallel to a longitudinal axis of the recuperator plate.

In a further aspect, there is provided a method for manufacturing a recuperator for a gas turbine engine, the method comprising: forming a first leading recess adjacent a first leading edge of a first thermally conductive sheet and forming a second leading recess adjacent a second leading edge of a second thermally conductive sheet, the first and second thermally conductive sheets being components of a recuperator plate; mating the first leading recess of the first thermally conductive sheet with the second leading recess of the second thermally conductive sheet; following the step of mating, joining the first and second leading sheet edges and a first and second trailing sheet edges thereby forming a recuperator plate, the first and second leading recesses forming a trough extending along a leading edge of the recuperator plate in a direction substantially parallel to a longitudinal axis of the recuperator plate.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine;

FIG. 2 is a partial cross-sectional view of the gas turbine engine of FIG. 1, showing a recuperator in accordance with an embodiment;

FIG. 3 is a cross-sectional view of the recuperator of FIG. 2;

FIG. 4 is a perspective view of a recuperator segment of FIG. 3;

FIG. 5 is a perspective view of a recuperator plate of FIG. 4;

FIG. 6 is a partial cross-sectional view of the recuperator segment of FIG. 4;

FIG. 7 is a close-up view of FIG. 6 showing a laminar flow in accordance with an embodiment; and

FIG. 8 is a flowchart of a method for manufacturing a recuperator in accordance with an embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a gas turbine engine 10 of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication, a fan 12 through which ambient air is propelled, a compressor section 14 for pressurizing the air, a combustor 16 in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section 18 for extracting energy from the combustion gases. The combustion gases flowing out of the combustor 16 circulate through the turbine section 18 and are expelled through an exhaust duct 24.

Although illustrated as a turbofan engine, the gas turbine engine 10 may alternatively be another type of engine, for example a turboprop or turboshaft engine, also generally comprising in serial flow communication a compressor section, a combustor, and a turbine section, and further including an exhaust duct through which the hot turbine gases are expelled.

Referring to FIG. 2, a recuperator 30 extends across the exhaust duct 24, such that the exhaust gas from the turbine section 18 circulates therethrough. As will be discussed further below, the recuperator 30 may then use the hot exhaust gas from the engine 10 to heat compressed air exiting from the compressor 14 and/or fan 12 prior to circulation of the compressed air to the combustion chamber 16. In this manner, the fuel efficiency of the engine 10 is improved while its infrared signature is minimized.

Referring to FIG. 3 and FIG. 4, the recuperator 30 comprises a plurality of recuperator segments 40, which illustratively function and are connected to the engine 10 independently from one another. Structural supports 42 may be provided between adjacent ones of the recuperator segments 40 to provide structural stability. The recuperator segments 40 are positioned relative to one another so as to together define the substantially annular shape of the recuperator 30.

Each recuperator segment 40 comprises a plurality of recuperator plates 44 arranged in a stacked relationship along an axis A. To provide structural stability, the stack may be mounted on one or more backing members 46, such as a frame, chassis or endplate, which does not impede the flow of fluid through the recuperator segment 40.

Referring to FIG. 5 in addition to FIG. 2 and FIG. 3, each recuperator plate 44 is elongate and extends along a longitudinal axis B. It should however be understood that each recuperator plate 44 may have some axial curvature by shaping and/or angling thereof to introduce some deviation or curvature to the axis B. Each recuperator plate 44 comprises a leading peripheral edge 48 and a trailing peripheral edge 50 opposite the leading edge 48. With the recuperator 30 extending across the exhaust duct (reference 24 of FIG. 1) of the engine 10, a radial turbine exhaust gas flow 52 is conducted through the recuperator segments 40 and received at the leading edges 48 of the recuperator plates 44. The flow 52 may subsequently progress through the recuperator plates 44 of each recuperator segment 40, as will be discussed further below, and is discharged at the trailing edges 50. A flow 53 of a secondary fluid, such as low-temperature pressurized air output from the compressor 12, may further be drawn, conducted, or otherwise received into the recuperator plates 44. Air flow 53 may be conducted into the recuperator plates 44 in a generally transverse direction to the exhaust gas flow 52. In particular and as will be detailed below, the air flow 53 passes through the recuperator plates 44 in thermal conductive proximity with the exhaust gas flow 52 so as to effect heat exchange therewith. The exhaust gas flow 52 and the air flow 53 are therefore brought closer in temperature than upon entry to the recuperator 30. The hotter of the two fluid flows, e.g. the exhaust gas flow 52, may therefore be cooled while the cooler of the two fluid flows, e.g. the air flow 53, is heated.

Referring to FIG. 6 in addition to FIG. 5, each recuperator plate 44 illustratively comprises a pair of thermally conductive sheets 54 a, 54 b in sealed together relation. The sheets 54 a, 54 b, may be made of any suitable thermally conductive and suitable formable material(s), such as metal(s), ceramic matrix composite material(s), and the like, alone or in any combination(s), mixture(s), or concentration(s) suitable for providing heat exchange. The sheets 54 a, 54 b may be constructed to have a minimal thickness, thus achieving lightweight design and improved thermal efficiency. The sheets 54 a, 54 b may be joined together by welding, brazing, or any other suitable process.

A plurality of protrusions or corrugations as in 56 a, 56 b are illustratively formed on the surface of each sheet 54 a, 54 b. The protrusions 56 a, 56 b may be provided in a pattern along at least one dimension (e.g. length, width) of the sheets 54 a, 54 b so that the latter have a substantially undulated cross-sectional profile. Depending on the positioning and pattern of the protrusions 56 a, 56 b, the undulations in the cross-sectional profiles of the sheets 54 a, 54 b may extend widthwise, lengthwise, or any other direction. A first substantially elongate concavity or trough 58 a is further formed in the first sheet 54 a at the leading edge 48 a thereof while a second concavity 60 a is formed in the first sheet 54 a at the trailing edge 50 a thereof. Similarly, a first concavity 58 b is formed in the second sheet 54 b at the leading edge 48 b thereof while a second concavity 60 b is formed in the second sheet 54 b at the trailing edge 50 b thereof. Each concavity 58 a, 58 b, 60 a, 60 b extends along the leading and trailing edges in a direction parallel to the longitudinal axis B. In other words, the leading edge concavities 58 a, 58 b are disposed in a direction substantially transverse to the airflow through the recuperator plates, along the length of each leading edge of each recuperator plate. These leading and trailing edge concavities are disposed and oriented in the sheets 54 a, 54 b of the plates 44 such that they are generally parallel to one another. Further, the leading edge concavities 58 a, 58 b are disposed such that the concavities face the suction side of the plates 44 in the recuperator stack (the suction side being defined as a result of the hot turbine exhaust stream entering the recuperator stack at a positive incidence angle). By ensuring that the concavities face the suction side of the recuperator leading edge 48 of plates 44, the leading edge laminar bubble that is created is contained in the trough or concavity 58 a, 58 b, which energizes the boundary layer and allows the flow to re-attach immediately downstream of the trough, as depicted in FIG. 7. This ensures flow turning with limited pressure loss and increased heat transfer at the leading edge of the recuperator plates 44.

In order to form the protrusions 56 a, 56 b and the concavity 58 a, 58 b, 60 a, 60 b, the sheets 54 a, 54 b may be press-formed, bent, curled, cut, deformed, tooled, or otherwise machined. In one embodiment, the concavities 58 a, 58 b, 60 a, 60 b are formed during manufacturing of a given sheet 54 a, 54 b prior to forming the protrusions 56 a, 56 b. As such, the concavities 58 a, 58 b, 60 a, 60 b may serve as a centering and reference feature allowing for high accuracy in the relative positioning of the sheets 54 a, 54 b. Indeed, the concavities 58 a, 58 b, 60 a, 60 b provide means for accurately positioning a pair of sheets as in 54 a, 54 b relative to one another when forming each recuperator plate 44 and during brazing or welding of the plates. As illustrated in FIG. 6, the sheets 54 a, 54 b may be positioned in close proximity to one another so that corresponding concavities 58 a, 58 b, 60 a, 60 b nest or otherwise mate with one another. In particular, a convexly curved surface (not shown) of each concavity 58 a, 60 a of the first sheet 54 a may be conformed to a concavely curved surface (not shown) of each corresponding concavity 58 b, 60 b of the second sheet 54 b. Plate concavities 58 and 60 may then be formed by the mating of a pair of concavities 58 a, 58 b, 60 a, 60 b. In this position, the protrusions 56 a of the first sheet 54 a may further nest or be otherwise conformal fitted with the corresponding protrusions 56 b of the second sheet 54 b. Plate protrusions 56 may then be formed by the conformal fitting of a pair of protrusions 56 a, 56 b. The leading edge 48 a of the first sheet 54 a may then be welded, brazed, or otherwise attached to the leading edge 48 b of the second sheet 54 b while the trailing edge 50 a of the first sheet 54 a is welded to the trailing edge 50 b of the second sheet 54 b, thereby forming brazed areas 62.

The leading edge concavities 58 a, 58 b and the trailing edge concavities 60 a, 60 b of the recuperator plates 44 also provide an accurate positioning reference which can be used, once these concavities or longitudinally extending troughs are created in the plates, as a reference guide for subsequently performed manufacturing operations carried out to create the completed recuperator plates 44, such as forming, trimming, and assembly, brazing, etc. The performance of the thus formed recuperator segment (reference 40 in FIG. 3) and accordingly the overall performance of the engine 10 are therefore improved. The provision of the concavities 58 a, 58 b, 60 a, 60 b further improves the stiffness of the formed recuperator plate 44 at the leading edge 48 and trailing edge 50 thereof. The geometry of the leading and trailing edges 48, 50 can therefore be maintained while the rest of the plate 44 deforms under thermal and/or pressure loads. As such, buckling of the plate 44 may be prevented.

When the sheets 54 a, 54 b are coupled as shown in FIG. 6, a fluid channel 64 is defined by the spacing between adjacent surfaces (not shown) of the sheets 54 a and 54 b. In addition, once each recuperator plate 44 is formed, the plurality of plates 44 are then stacked along the axis A, resulting in the fluid channels 64 being stacked in close proximity to one another. In this configuration, a number of interior compartments or interstitial layers (more generally “interstices”) 66 are further formed between adjacent recuperator plates 44. The shape of the interstices 66 may be defined by the shape and spacing between the protrusions as in 56 of adjacent recuperator plates 44. In particular, the protrusions 56 of adjacent plates 44 may oppose so that each protrusion 56 of one plate 44 is sized to accommodate a corresponding recess 68 between adjacent protrusions 56 of an adjacent plate 44. Each interstice 66 may then be defined by the spacing between a concavely curved surface (not shown) of a protrusion 56 of the one plate 44 and a concavely curved surface (not shown) of a recess 68 between adjacent protrusions 56 of the adjacent plate 44.

The fluid channels 64 may be suitable to receive and conduct therethrough the air flow 53 while the interstices 66 may be suitable to receive and conduct therethrough the gas exhaust flow 52. In particular, the fluid channels 64 are illustratively sealed from the external environment, including being sealed from the interstices 66. The exhaust gas flow 52 can therefore be conducted through the recuperator 30 without admixture or interminglement with the air flow 53. As the air flow 53 passes through the fluid channels 64 in thermal conductive proximity with the exhaust gas flow 52 passing through the interstices 66, heat exchange is effected between the air flow 53 and the exhaust gas flow 52. In addition, due to the undulating pattern of the protrusions 56 on each recuperator plate 44, an undulating flow path is formed in the fluid channels 64. Fluid turbulence, and therefore fluid mixing, is thus increased within the fluid channels 64 to promote heat exchange between the air flow 53 and the exhaust gas flow 52. It should be understood that while it may be advantageous in some embodiments for the fluid channels 64 to conduct a relatively high-pressure, low-temperature fluid, e.g. the air flow 53, in comparison to a relatively low-pressure, high-temperature fluid, e.g. the exhaust gas flow 52, conducted through the interstices 66, the recuperator 30 is not limited to such usage.

Referring now to FIG. 7, upon the exhaust gas flow 52 being received at the leading edge 48 of the recuperator plates 44 and reaching the concavities 58, laminar bubbles 68 are formed. When such laminar bubbles 68 form, the gas flow 52 no longer follows the curvature of the recuperator plates 44 and the laminar boundary layer separates from the surface of the recuperator plates 44. Still, due to the residual swirl of the exhaust gas flow 52, the latter illustratively is received at the leading edges 48 of the recuperator plates 44 segment 40 at a positive incidence angle (not shown) such that the laminar bubbles 68 are contained in the concavities 58. As a result, the boundary layer is energized and flow re-attachment occurs behind the laminar bubbles 68 immediately downstream of the concavities 58. The re-attachment of the exhaust gas flow 52 to the plates 44 then ensures flow turning with reduced pressure loss and increased heat transfer at the leading edge 48 of the plates 44. Leading edge aerodynamics on the recuperator segment 40 are further significantly improved, thus improving the overall efficiency of the recuperator 30.

Referring to FIG. 8, a method 100 for manufacturing a recuperator will now be described. The method 100 comprises the step 102 of forming troughs at the leading and trailing edges of each one of a plurality of thermally conductive sheets. The next step 104 may then be to form corrugations in each sheet. The troughs and corrugations may be formed by at least one of press-forming, bending, curling, cutting, deforming, tooling, or otherwise machining the sheets, as discussed above. The next step 106 may then be to mate the troughs of a first sheet to those of a second sheet in order to position the first sheet relative to the second sheet. The first and second sheet may then be joined at step 108 by brazing the leading and trailing edges thereof, thereby forming a recuperator plate. A plurality of the thus formed recuperator plates may then be stacked at step 110 to form each recuperator segment of the recuperator.

The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims. 

1. A method for manufacturing a recuperator for a gas turbine engine, the method comprising: forming at least one recuperator plate, the recuperator plate extending in a longitudinal direction between an upstream and a downstream end spaced apart along a longitudinal axis, the recuperator plate extending in a transverse direction between a leading edge and a trailing edge thereof, each of the leading edge and the trailing edge extending longitudinally between the upstream and the downstream edges, the transverse direction being substantially perpendicular to the longitudinal direction defined by the longitudinal axis, forming the recuperator plate including: providing first and second thermally conductive sheets, respectively having a first sheet leading edge and a first sheet trailing edge, and a second sheet leading edge and a second sheet trailing edge; forming a first leading recess adjacent the first sheet leading edge of the first thermally conductive sheet, and forming a second leading recess adjacent the second sheet leading edge of the second thermally conductive sheet; mating the first leading recess of the first thermally conductive sheet with the second leading recess of the second thermally conductive sheet; and following the step of mating, joining the first and second thermally conductive sheets together to form the recuperator plate with at least one fluid channel therein, the mated first and second leading recesses forming a trough extending along a leading edge of the recuperator plate in a direction substantially parallel to a longitudinal axis of the recuperator plate.
 2. The method of claim 1, further comprising forming the at least one fluid channel of the recuperator plate with a height that is non-uniform along the transverse direction and which narrows toward the leading edge, the at least one fluid channel defining a cross-sectional profile having said height in a direction perpendicular to the longitudinal direction and the transverse direction.
 3. The method of claim 1, further comprising forming a plurality of said recuperator plates and arranging the plurality of the recuperator plates in a stacked relationship to form an air-to-air heat exchanger, the recuperator plates being spaced apart to define therebetween a plurality of interstices adapted to direct therethrough at least one first stream received at a leading plate edge of the recuperator plates and a plurality of fluid channels adapted to direct therethrough at least one second stream to effect heat exchange between the at least one first stream and the at least one second stream.
 4. The method of claim 1, further comprising forming a first trailing recess adjacent the first trailing edge of the first sheet and forming a second trailing recess adjacent the second trailing edge of the second sheet, and wherein the first and second trailing recesses are substantially parallel to the first and second leading recesses and to the longitudinal axis of the recuperator plate.
 5. The method of claim 1, further comprising forming a first plurality of protrusions in the first sheet and a second plurality of protrusions in the second sheet and conforming a convexly curved surface of each one of the second plurality of protrusions to a concavely curved surface of each one of the first plurality of protrusions prior to joining the first and second leading sheet edges and the first and second trailing sheet edges.
 6. The method of claim 1, further comprising forming the trough on a suction side of the recuperator plate to contain a leading edge laminar flow bubble therein and cause re-attachment of laminar flow immediately downstream of the trough extending along the leading edge of the recuperator plate.
 7. The method of claim 1, wherein the step of joining the first and second thermally conductive sheets together includes brazing the first sheet leading edge to the second sheet leading edge and the first sheet trailing edge to the second sheet trailing edge. 